1. Field of the Invention
The present invention relates to a process for preparing ultrafine crystalline barium titanate powder having a small particle size and a spherical shape to be used as a main constituent in the preparation process of MLCC (multilayer ceramic capacitor), filters and other components for the next generation microwave communication equipments.
2. Description of the Background Art
Barium titanate, expressed chemically as BaTiO3, is a ferroelectric material having a Perovskite structure. BaTiO3has been used as the main raw material for MLCC, filters, thermistors and varistors due to its extremely high dielectric constant, relatively cheap price, and high thermal stability. Recently, electronic or communication devices have become more sophisticated and denser. The techniques of preparing powder with superior crystallinity, purity and small particle size is industrially very meaningful since current development trend is focused on miniaturizing the size of the products while increasing the performance. For example, devices prepared with barium titanate powder of a smaller particle size tend to show a lower failure rate and higher dielectric constant due to the smaller grain structure. Therefore, smaller number of layers are needed thus increasing the efficiency of the raw materials. In addition, less energy and costs are required since lower temperature is needed to sinter for dense nanocrystals. Moreover, it is well believed that the MLCC, filters and other devices, which are prepared with ultrafine powders, would also have an excellent capability also in the microwave range for next generation communication.
Generally, barium titanate powders are produced commercially by two different methods. A solid-state reaction method has been well known since the early days. In this method, titanium oxide and barium carbonate powders are mixed and reacted at high temperatures (over 1000xc2x0 C.) to produce barium titanate powders. Since this method has an advantage in that the production cost of barium titanate is low, it has been mainly used commercially. However, the minimum size of the powder is around 1 micron for the solid-state reaction at high temperatures, and the morphology of the particle is also heterogeneous. Therefore, it is not suitable for devices with an aim of miniturization.
Another method is the oxalate precipitate method that has been becoming more popular these days in the United States. This method is a simple chemical synthesis and has an advantage of high yields. However, It is not easy to control the size and the degree of particle aggregation to a desirable level. Since the stability of barium/titanium oxalate is high, it requires high temperature thermal treatment to produce highly crystalline barium titanate. Therefore, the mean particle size of the final particles is at least 0.5 micron.
Accordingly, an object of the present invention is to provide a method of manufaturing barium titanate particles. It is another object of the present invention to provide a process for reducing the particle size and increasing the crystallinity of barium titanate compared to those manufactured by the conventional solid state reaction method or the oxalate method.